The present invention relates to a packer type groundwater sampling system, which can be used for an apparatus for sampling groundwater in a borehole or a well or for an apparatus for carrying out test at any desired depth in a borehole or a well. The invention also relates to a method for sampling groundwater using such a system.
Continuous water sampling method has been used for sampling groundwater in the past. A typical method is a pumping-up method. In this method, a pump is installed in a probe placed in a borehole, and groundwater in a water sampling section is continuously sampled and brought up to the ground surface. Also, an air-lift method using air pressure from ground surface is known as one of the continuous water sampling methods.
On the other hand, a batch style water sampling method has also been proposed (Japanese Utility Model Publication Laid-Open 3-69090 and Japanese Patent Publication Laid-Open 6-201542). In this method, a completely sealed water sampling container is used to characterize groundwater chemistry and water can be sampled under in-situ condition.
Also, a water sampling apparatus has been proposed, which combines the above two methods to overcome the disadvantages of these methods (Japanese Patent Publication Laid-Open 6-193101).
The pumping-up method, i.e. the most typical of the continuous water sampling methods, is higher in working efficiency than the batch style water sampling method. However, because pumping ability of the pump is effective for the depth of several hundreds of meters in the current technical level, water cannot be pumped up if the groundwater level in borehole is lower than the limit of the pumping ability.
Also, because it is impossible to sample groundwater under in-situ condition from structural reason, there are problems in that dissolved gas in the groundwater is released at the ground surface when it is opened to the atmospheric air due to pressure change. Further, because water is sampled continuously for long time, load applied on the pump is high, and this extensively reduces durability of the pump.
In the air-lift method, compressed air sent from the ground surface is used, and it is impossible to sample groundwater in in-situ condition.
By the batch style water sampling method, it is possible to sample formation water under in-situ condition without disturbing geological environment where the groundwater is present. However, it is not possible to strictly judge whether the formation water under in-situ condition has been sampled or not unless there is the function to confirm that the pressure in the container for sampling groundwater has reached the same level as the underground condition.
Also, in the practical procedure, drilling fluid has been used for the drilling of boreholes and the groundwater will be contaminated by this fluid. The absence of drilling fluid in water has been checked by continuous monitoring of:
(1) concentration of tracers (e.g. Uranine dye or Li) which are introduced into the drilling fluid; and PA0 (2) concentration of chemical components.
The absence of tracers, or constant concentrations of chemical components can be regarded as an indication of the absence of drilling fluid. Water sampling volume per batch is also low, and much time is required to carry out the work by this method alone, and there is also problems in working efficiency.
On the other hand, the combination of the continuous water sampling method and the batch style water sampling method is not yet used in practical application, but it overcomes the disadvantages of these two methods. By this method, however, formation water necessary for water quality analysis is sampled by one time in the batch style water sampling method. If the required quantity has not been sampled, the water sampling section is sealed off for once and the water is mixed with the groundwater of the other level when the second batch style water sampling is carried out. Thus, the continuous water sampling must be carried out again. Further, in case water chemistry is to be monitored over a long period, the continuous water sampling and the batch style water sampling must be performed each time, and problems arise about quality or economic feasibility of the sampled groundwater. Also, there are problems in that the formation water sampled and brought to ground surface by the batch style water sampling method cannot be easily taken out and transported.
In testers in a borehole, there are hydrological tester, pore water pressure measuring apparatus, flow direction and velocity measuring apparatus, borehole expansion tester, etc. in addition to groundwater sampler. In major functions of these apparatuses, there are the following problems at present:
(a) Packer structure
The tester in the borehole normally uses packer or mechanical packer based on water pressure or air pressure to set up a measuring section. As depth increases, water packer is used because of safety and maneuverability. In the conventional type water packer structure, there are the following problems:
Because diameter of water supply hose in the packer expansion system is small, pressure loss inside the pipe increases, and longer time is required for expansion of the packer. PA1 To expand the packer, water in hose (such as tap water), and not in-hole water (i.e. mixture of groundwater at various depths in a borehole), is used in many methods. In this case, if leakage occur, water other than the in-hole water is brought into the hole, and this results in contamination of the groundwater in the borehole. PA1 When the level of groundwater in borehole is lowered, packer is spontaneously expanded due to water pressure from ground surface to the level of groundwater. As a result, it is difficult to recover the packer. PA1 In many cases, water supply hose of the packer expansion system is installed outside casing pipe. This causes damage of wall of borehole and makes it difficult to recover the apparatus. Also, much time is required for installing hoses and cables, leading to lower working efficiency. PA1 Because water hose is present in a packer expansion circuit system, volume inside the hose and volume change due to creeping of hose are also included in water injection quantity, and it is not possible to accurately identify quantity of water injected into the packer itself.
(b) Installation of pipes and signal cable
Also, it is difficult to identify quantity of the water extracted from the packer.
To solve the above problems, it is an object of the present invention to develop and provide a water sampling system, by which it is possible to sample formation water under in-situ condition at deeper depth reliably, efficiently and economically without disturbing geological environment of groundwater present in underground formation by means of borehole.
It is another object of the present invention to limit a water sampling section to a certain depth, to quickly discharge drilling water and other water mixed with water of the other level from the sampling section and to replace them with the formation water.
It is still another object of the present invention to sample the formation water under in-situ condition.
It is another object of the present invention to sample the formation water by batch style water sampling method continuously and by many times without carrying out continuous water sampling after the groundwater in the water sampling section has been replaced with the formation water.
It is another object of the present invention to make it possible to confirm that pressure in a water sampling container is in equilibrium with water pressure environment where the formation water has been present in the batch style water sampling method and to confirm water sampling volume in the water sampling container in order to reliably perform water sampling under in-situ condition.
It is still another object of the present invention to make it possible to easily take out formation water sampled and brought to ground surface by the batch style water sampling method and to transport the water under in-situ condition.
It is another object of the present invention to make the packer expandable by utilizing in-hole water in order to reliably and safely limit the water sampling section without disturbing the geological environment where the groundwater is present.
It is still another object of the present invention to make it possible to sample and bring groundwater safely to ground surface by protecting major functional components even when it is not possible to recover the packer system due to collapse occurring in the borehole.